MMP9 and neoplasm: They promote tumor immunosuppression, proliferation, angiogenesis, and metastasis via the expression of factors such as the programmed cell death receptor ligand 1 (PD-L1), arginase-1, neutrophil elastase (NE), matrix metallopeptidase 9 (MMP9), chemokine receptors (CXCR1 and CXCR2), and vascular endothelial growth factor (VEGF) [8, 9].